Patients may also not want to dwell on some aspect of care that's in the past, researcher says.

Many cancer patients who'd had problems with their treatment never said anything to the doctor they thought was responsible - and almost none formally reported the problems to the hospital, according to a survey of cancer patients.

In the study, published in the Journal of Clinical Oncology, patients cited delays in treatment, surgical complications and other issues related to medical care, in addition to communication barriers or breakdown between them and their doctors, as the most common potentially harmful problems.

Lead author Kathleen Mazor, from Meyers Primary Care Institute and the University of Massachusetts Medical School in Worcester, said there may be many reasons for this.

"Sometimes there's a situation where they're really still thankful for the care that they got, and so they don't want to hurt anybody by saying, 'Everything was great, except...' Or they don't want to do harm to their relationship with their doctor," she added.

Patients may also not want to dwell on some aspect of care that's in the past, she said.

"When people are undergoing something like cancer, they really feel they need to put all their energy on looking forward. They're thinking about getting better, moving forward, dealing with cancer and coming out the other end."

In interviews with about 400 breast and colon cancer patients, more than one in five said something "went wrong" during their cancer care that could have been prevented - and caused or could have caused them physical or psychological harm.

Seventy-eight patients, almost all women who'd been treated for breast cancer, completed surveys with Mazor and her team about those problems.

About three-quarters of them cited a communication problem with their doctor, such as not getting enough information or getting inaccurate information about their cancer. Specific examples included not being told about treatment options or being told their cancer would lead to death, only to have test results reveal it was treatable.

Half said something went wrong during their medical care itself, such as surgical problems requiring additional surgery, infections or perceived delays in treatment and diagnosis.

Almost all cancer patients said that the problems with their doctor, whether communication-related or medical, had resulted in psychological harms such as anger, fear and distress. The majority also cited physical harms like pain and the need for additional treatment.

Despite those consequences, just one-third of people the researchers interviewed said they'd discussed the harmful event with the doctor or nurse they believed was responsible.

Ten of them reported the problem to the hospital administration, Mazor's team wrote.

The message is that patients should speak up, she said.

"Sometimes patients think that something has gone wrong and it hasn't. But if you never tell anybody... they never have a chance to say 'This is how it always goes' or 'We couldn't prevent that,'" she said.